Measuring and understanding individual differences in cognition

Abstract

Individuals vary in their cognitive performance. While this variation forms the foundation of the study of human psychometrics, its broader importance is only recently being recognized. Explicitly acknowledging this individual variation found in both humans and non-human animals provides a novel opportunity to understand the mechanisms, development and evolution of cognition. The papers in this special issue highlight the growing emphasis on individual cognitive differences from fields as diverse as neurobiology, experimental psychology and evolutionary biology. Here, we synthesize this body of work. We consider the distinct challenges in quantifying individual differences in cognition and provide concrete methodological recommendations. In particular, future studies would benefit from using multiple task variants to ensure they target specific, clearly defined cognitive traits and from conducting repeated testing to assess individual consistency. We then consider how neural, genetic, developmental and behavioural factors may generate individual differences in cognition. Finally, we discuss the potential fitness consequences of individual cognitive variation and place these into an evolutionary framework with testable hypotheses. We intend for this special issue to stimulate researchers to position individual variation at the centre of the cognitive sciences.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.

Keywords: cognition; evolution; heritability; individual differences; personality; plasticity.

Figure 1.

Conceptual representation of the four research approaches that can inform our understanding of the causes and consequences of individual variation in cognitive abilities. (a) Multiple tests: several variants of a test (A, B, C) are used in order to assess convergent validity. Repeatability of performance is also estimated, at least for the focal test (B1, B2, B3). (b) Multiple states: a test (B) is administered under varying levels of internal or external states. These could be experimentally manipulated (e.g. food deprivation) or observational (e.g. samples at 0, 100 and 200 days during development), in order to assess the robustness of individual ranks in performance and identify drivers of plasticity in cognitive ability. (c) Multiple traits: other traits are quantified, in order to identify phenotypic and genetic correlations with the cognitive ability of interest (B). (d) Multiple fitness proxies: several components of lifetime reproductive success are measured in order to examine potential trade-offs amongst them, or contrasting links between fitness proxies with the cognitive ability of interest (B).